1. Technical Field
One or more embodiments of the present invention generally relate to temperature control. In particular, certain embodiments relate to overheat detection in thermally controlled devices.
2. Discussion
The popularity of computing systems continues to grow and the demand for mobile computing systems such as notebook personal computers (PCs), personal digital assistants (PDAs) and wireless “smart” phones, in particular, has experienced historical escalations. While the trend toward smaller computers and faster processing speeds has been desirable to consumers, it presents a number challenges to computer designers as well as manufacturers. A particular area of concern relates to overheating.
It is well documented that a computer processor running at a higher speed tends to consume more power and generate more heat than a similarly situated processor running at a lower speed. The increase in temperature can negatively impact the performance of the processor as well as the performance of nearby components. For example, device speed and long term reliability can deteriorate as temperature increases. If temperatures reach critically high levels, the heat can cause malfunction, degradation in lifetime or even permanent damage to the part.
Modern approaches to on-die overheat detection in computer processors involve the establishment of a temperature “guard band” defined by a lower temperature threshold and an upper temperature threshold. An internal temperature of the processor is monitored and when the internal temperature crosses the lower threshold of the guard band, thermal management techniques such as clock throttling or voltage/frequency scaling are activated. FIG. 1A shows a thermal management plot 10 in which a guard band is defined by a lower control temperature threshold 12 and an upper shutdown temperature threshold 14. When the internal temperature curve 16 reaches the lower threshold 12, thermal management is activated, which if successful, brings the average temperature 18 down over time. FIG. 1B, on the other hand, shows a plot 21 having an internal temperature curve 20 in which thermal management is unsuccessful and the average temperature 22 increases over time. In such a case, the upper threshold 14 of the guard band is used to signal a system shutdown in order to prevent catastrophic failure. While such an approach has been acceptable under certain circumstances, there remains considerable room for improvement.
For example, conventional overheat detection approaches depend upon system shutdowns associated with the upper threshold 14 as the sole mechanism for protecting against unsuccessful thermal management. As a result, system shutdowns due to overheating can appear to the user as being rather abrupt. For example, in some cases, data is lost due to a lack of advance notice of the impending shutdown. Furthermore, it is common to design the guard band to be fairly large in order to afford the thermal management techniques sufficient time to bring the average temperature down before a system shutdown occurs. The larger guard band essentially results in a smaller thermal envelope and allows for less processing resources because a higher performing processor cannot be used.